Planetary gear type transmission mechanism

ABSTRACT

A planetary gear type transmission mechanism reduces frictional resistance at all forward speed ratio. The transmission mechanism includes an input shaft, an output shaft, a first planetary gear set, a second planetary gear set and a friction means. The friction means includes a plurality of friction elements for determining power transmission route through at least one of the first and second planetary gear sets for establishing a plurality of forward speed ratios. At any forward speed ratio all gear elements of the first and second planetary gear sets except for the gear elements integrally coupled with the output shaft rotate in the same direction as that of the input shaft at speed less than the input shaft.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a planetary gear type transmissionmechanism, for example, to be used for an automatic transmission.

2. Description of the Related Art

Japanese Patent Application Laid Open No. 64-30950 discloses a planetarygear type transmission mechanism, in which two pairs of planetary gearsets are employed for establishing forward five speed ratios. In thedisclosed transmission mechanism, one of the planetary gear sets isconstructed in a double pinion type, in which two planet pinion gearsmeshing with each other are provided. The other of the planetary gearsets is constructed in a single pinion type, in which a single planetpinion is employed.

The disclosed conventional transmission mechanism is shown in FIG. 1 byskeleton diagram. As seen in this FIG. 1, the double pinion typeplanetary gear set G1 includes a first sun gear S1, a first internalring gear R1, and a pinion carrier PCl rotatably supporting first outerand inner planet pinion gears P0, P1. The first outer planet piniongears P0 meshes with the first internal ring gear R1 and the first innerplanet pinion gears P1 meshes with the first sun gear S1.

On the other hand, the single pinion type planetary gear set G2 includesa second sun gear S2, a second internal ring gear R2, and a secondpinion carrier rotatably supporting second planet pinion gears P2 meshedwith the gears S2 and R2.

The planetary gear sets G1 and G2 are related to each other and to aninput and output shafts 10 and 12 through three clutches C1, C2 and C3and three brakes B1, B2 and B3 as shown in FIG. 1. The engagingactuation of these clutches and brakes with the combination shown inFIG. 2 (refer to "◯" marks) provides the corresponding five forward gearpositions and one reverse gear position, since the first pinion carrierPCl and the second sun gear S2 are coupled with each other to form afirst rotating unity and the first sun gear S1 and the second internalring gear R2 are coupled with each other to form a second rotatingunity.

In the foregoing construction, the relationship among rotation speedratios of constructional gear elements of the both planetary gear setsto the input shaft is as shown in FIGS. 3 to 8 at each gear positions,i.e. the first, second, third, fourth and fifth gear positions forforward and the reverse gear position. FIGS. 3 to 8 are alignment chartsin which constructional gear elements of each planetary gear set arepositioned horizontally according to the gear ratio of the internal ringgear teeth number and the sun gear teeth number, a line extending acrossthe vertical axes corresponding to the constructional gear elements ofthe planetary gear set represents the rotation speed ratio of eachconstructional gear element at the crossing points to the above verticalaxes. Of course, the rotation speed ratio 0 represents the state inwhich the relevant constructional element is fixed, 1 represents thestate, in which the relevant constructional element rotates in the samedirection as that of the input shaft (forward direction) at the samespeed as that of the input shaft, and the negative value represents thestate, in which the relevant constructional element rotates in oppositedirection to the input shaft (reverse direction).

Explaining, for example, the first gear position as shown in FIG. 3, thefirst sun gear S1 and the second internal ring gear R2 are fixed byengaging actuation of the first brake B1, the first pinion carrier PCland the second sun gear S2 are rotated forwardly at the same speed asinput speed, i.e., the rotation speed of the input shaft 10 by engagingactuation of the first clutch C1. For the above, as appreciated fromFIG. 3 the second pinion carrier PC2 is rotated forwardly, butremarkably reduced in rotation and this reduced rotation at output speedis delivered from the second pinion carrier PC2 to the output shaft 12coupled therewith.

Such prior planetary gear type transmission mechanism described abovehas following problems.

At the second gear position as shown in FIG. 4, the first pinion carrierPCl and the second sun gear S2 are driven to rotate at approximately thesame speed as the input speed in opposite direction to the inputrotation. Furthermore, at the fifth gear position as shown in FIG. 7,the first sun gear S1 and the second internal ring gear R2 are driven torotate at a speed approximately twice of the input rotation. With suchconstruction, because of presence of the elements driven in the oppositedirection to the input rotation, and of presence of the elementsrotating at high speed, friction plates arranged with small clearanceswithin the clutches and brakes are rotated relatively to each other athigh speed to increase in frictional resistance under disengagecondition of the clutches and brakes. On the other hand, the elementsrotating at high speed must be supported by bearings of sufficientstrength for withstanding centrifugal force and for withstanding highspeed rotation, which are accessibly expensive.

Furthermore, in the disclosed construction, at the fifth gear positionof high frequency in use both of the planetary gear sets are used forpower transmission as appreciated in FIG. 7. Such arrangement is notdesirable because of possibility of causing gear noise and low powertransmission efficiency. Particularly, since the fifth gear position ismost frequently used at the normal vehicular driving condition, problemof the gear noise and the low power transmission efficiency issubstantial.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve the problems in theprior art.

Another object of the invention is to provide a planetary gear typetransmission mechanism which can suppress gear noise and improve powertransmission efficiency.

A further object of the invention is to provide a planetary gear typetransmission mechanism which can eliminate any elements rotating in theopposite direction to the input rotation and any elements rotating ataccessibly high speed over the input rotation, other than outputelement.

In order to accomplish above-mentioned and other objects, it is a firstaspect of the invention, a planetary gear type transmission mechanismcomprises:

an input member to be supplied rotation from a power supply;

an output member for delivering rotation changed in speed at an selectedspeed ratio;

a first gear set including a gear element constantly coupled with saidinput member for rotation therewith; and

a second gear set including a gear element constantly coupled with saidoutput member for rotation therewith;

friction means including a plurality of friction elements fordetermining power transmission route through at least one of said firstand second gear sets for establishing a plurality of speed ratiosbetween the input and output members;

other gear elements of the first and second gear sets being coupled witheach other and the friction elements being arranged, in such manner thatall gear elements of the first and second gear sets except for said gearelement constantly coupled with the output member rotates in the samedirection as that of the input member at speed less than the inputmember upon selection of any forward speed ratio.

In one example of the above planetary gear type transmission mechanismin accordance with the invention, it is preferred that the highest speedratio of said forward speed ratios is established with the second gearset is exclusively active for transmitting rotation of the input memberto the output member. The highest speed ratio is realized, for example,by connecting the gear element of the first gear set constantly coupledwith the input member and any one of gear elements of the second gearset for direct power transmission of the input rotation to the secondgear.

Such special construction, at the highest speed ratio most frequentlyused at normal vehicular driving condition, provides high powertransmission efficiency, since the first gear set is not active forpower transmission at all.

According to a second aspect of the invention, a planetary gear typetransmission mechanism comprises:

an input shaft;

an output shaft;

a first planetary gear set including a first sun gear, a first internalring gear, a first outer planet pinion gears and a first inner planetpinion gears meshed with each other, and a first pinion carrierrotatably supporting said first outer planet pinion gears and said firstinner planet pinion gears, said first outer planet pinion gears eachmeshing with said first internal ring gear, said first inner planetpinion gears each meshing with said first sun gear, and said firstpinion carrier being constantly coupled with said input shaft;

a second planetary gear set including a second sun gear, a secondinternal ring gear, a second planet pinion gears each meshing with bothof said second sun gear and said second internal ring gear, and a secondpinion carrier rotatably supporting said second planet pinion gears, andsaid second internal ring gear being constantly coupled with said outputshaft; and

a friction means including first, second, third and fourth clutches andfirst, second and third brakes, of which said first clutch connects anddisconnects the unity of said input shaft and said first pinion carrierto and from said first sun gear for selected speed ratio, said secondclutch connects and disconnects the unity of said input shaft and saidfirst pinion carrier to and from said second sun gear for selected speedratio, said third clutch connects and disconnects the unity of saidfirst internal ring gear and said second pinion carrier to and from saidsecond sun gear for selected speed ratio, said fourth clutch connectsand disconnects the unity of said input shaft and said first pinioncarrier to and from the unity of said output shaft and said secondinternal ring gear for selected speed ratio, said first brake connectsand disconnects said first sun gear to and from a stationary member forselected speed ratio, said second brake connects and disconnects saidsecond sun gear to and from the stationary member for selected speedratio, and said third brake connects and disconnects the unity of saidsecond pinion carrier and said first internal ring gear to and from thestationary member for selected speed ratio.

According to the invention, in the above planetary gear typetransmission mechanism, said first clutch is altered to connect anddisconnect the unity of said input shaft and said first pinion carrierto and from the unity of said first internal ring gear and said secondpinion carrier for the selected speed ratio.

According to the invention, moreover, in the above planetary gear typetransmission mechanism, said third clutch is altered to connect anddisconnect the unity of said first internal ring gear and said secondpinion carrier to and from the unity of said output shaft and saidsecond internal ring gear for the selected speed ratio.

According to the invention, still moreover, in the above planetary geartype transmission mechanism, said fourth clutch is altered to connectand disconnect said first sun gear to and from said second sun gear forthe selected speed ratio.

Preferably, all of the described planetary gear type transmissionmechanism further comprises a one-way clutch arranged in series withsaid second clutch for easiness of shift between relevant speed ratios.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a skeleton diagram showing a prior art of a planetary geartype transmission mechanism;

FIG. 2 is a table showing relationship of friction elements to beengaged and gear positions established thereby as well as relevant speedratios in the prior art in FIG. 1;

FIG. 3 is an alignment chart at the first gear position for the aboveprior art;

FIG. 4 is an alignment chart at the second gear position for the priorart;

FIG. 5 is an alignment chart at the third gear position for the priorart;

FIG. 6 is an alignment chart at the fourth gear position for the priorart;

FIG. 7 is an alignment chart at the fifth (over-drive) gear position forthe prior art;

FIG. 8 is an alignment chart at the reverse gear position for the priorart;

FIG. 9 is a skeleton diagram showing the first preferred embodiment of aplanetary gear type transmission mechanism according to the presentinvention;

FIG. 10 is a table showing relationship between friction elements to beengaged and gear positions established thereby as well as relevant speedratios in the construction as shown in FIG. 9;

FIG. 11 is an alignment chart for the above first example at the firstgear position;

FIG. 12 is an alignment chart for the first preferred embodiment of theplanetary gear type transmission mechanism at the second gear position;

FIG. 13 is an alignment chart for the first preferred embodiment of theplanetary gear type transmission mechanism at the third gear position;

FIG. 14 is an alignment chart for the first preferred embodiment of theplanetary gear type transmission mechanism at the fourth gear position;

FIG. 15 is an alignment chart for the first preferred embodiment of theplanetary gear type mechanism transmission at the fifth gear position;

FIG. 16 is an alignment chart for the first preferred embodiment of theplanetary gear type transmission mechanism at the reverse gear position;

FIG. 17 an alignment chart for the first embodiment of the transmissionmechanism at the fourth ear position established by modified combinationof the friction elements to be engaged;

FIG. 18 is a skeleton diagram showing the second embodiment of theplanetary gear type transmission mechanism according to the invention;

FIG. 19 is a skeleton diagram showing the third embodiment of theplanetary gear type transmission mechanism according to the invention;

FIG. 20 is a skeleton diagram showing the fourth embodiment of theplanetary gear type transmission mechanism according to the invention;

FIG. 21 is a skeleton diagram showing the fifth embodiment of theplanetary gear type transmission mechanism according to the invention;

FIG. 22 is a skeleton diagram showing the sixth embodiment of theplanetary gear type transmission mechanism according to the invention;

FIG. 23 is an alignment chart for the sixth embodiment of the planetarygear type transmission mechanism at the first gear position;

FIG. 24 is an alignment chart for the sixth embodiment of the planetarygear type transmission mechanism at the second gear position;

FIG. 25 is an alignment chart for the sixth embodiment of the planetarygear type transmission mechanism at the third gear position;

FIG. 26 is an alignment chart of the sixth embodiment of the planetarygear type transmission mechanism at the fourth gear position

FIG. 27 is an alignment chart for the sixth embodiment of the planetarygear type transmission mechanism at the fifth gear position;

FIG. 28 is an alignment chart for the sixth embodiment of the planetarygear type transmission mechanism at the reverse gear position;

FIG. 29 is a skeleton diagram showing the seventh embodiment of theplanetary gear type transmission mechanism according to the invention;

FIG. 30 is a skeleton diagram showing the eighth embodiment of theplanetary gear type transmission mechanism according to the invention;

FIG. 31 is a skeleton diagram showing the ninth embodiment of theplanetary gear type transmission mechanism according to the invention;

FIG. 32 is a skeleton diagram showing the tenth embodiment of theplanetary gear type transmission mechanism according to the invention;

FIG. 33 is a skeleton diagram showing the eleventh embodiment of theplanetary gear type transmission mechanism according to the invention;

FIG. 34 is a table showing relationship between elements to be engagedand gear positions established thereby in the eleventh embodiment of theplanetary gear type transmission mechanism;

FIG. 35 is an alignment chart for the eleventh embodiment of theplanetary gear type transmission mechanism at the first gear position;

FIG. 36 is an alignment chart for the eleventh embodiment of theplanetary gear type transmission mechanism at the second gear position;

FIG. 37 is an alignment chart for the eleventh embodiment of theplanetary gear type transmission mechanism at the third gear position;

FIG. 38 is an alignment chart for the eleventh embodiment of theplanetary gear type transmission mechanism at the fourth gear position;

FIG. 39 is an alignment chart for the eleventh embodiment of theplanetary gear type transmission mechanism at the fifth gear position;and

FIG. 40 is an alignment chart for the eleventh embodiment of theplanetary gear type transmission mechanism at the reverse gear position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, particularly to FIG. 9, the firstembodiment of a planetary gear type transmission mechanism according tothe present invention, includes an input shaft 10, an output shaft 12coaxially arranged thereto, a first planetary gear set G1, a secondplanetary gear set G2, a first clutch C1, a second clutch C2, a thirdclutch C3, a fourth clutch C4, a first brake B1, a second brake B2 and athird brake B3.

The first planetary gear set G1 near the input shaft 10 is of a doublepinion type construction which has a first sun gear S1, a first internalring gear R1, and a first pinion carrier PCl rotatably supporting firstouter planet pinion gears P0 and first inner planet pinion gears P1meshing with each other. The first outer planet pinion gears P0 are alsomeshed with the first internal ring R1. The first inner planet piniongears P1 are also meshed with the first sun gear S1.

On the other hand, the second planetary gear set G2 near the outputshaft 12 is of a single pinion type construction which has a second sungear S2, a second internal gear R2, and a second pinion carrier PC2rotatably supporting second planet pinion gears P2. The second planetpinion gears P2 are meshed with both of the second sun gear S2 and thesecond internal ring gear R2.

The first pinion carrier PCl is normally coupled with the input shaft 10to be constantly driven therewith by an output torque of a power supply,such as an automotive internal combustion engine. The second internalring gear R2 is normally coupled with the output shaft 12 so as todeliver the output torque of the transmission mechanism to a final drivenot shown through the output shaft 12. The first internal ring gear R1and the second pinion carrier PC2 are integrally coupled with each otherto be rotated as one unity.

The first clutch C1 is adapted to connect and disconnect the unity ofthe input shaft 10 and the first pinion carrier PCl to and from thefirst sun gear S1. The second clutch C2 is adapted to connect anddisconnect the unity of the input shaft 10 and the first pinion carrierPCl to and from the second sun gear S2. The third clutch C3 is adaptedto connect and disconnect the unity of the first internal ring gear R1and the second pinion carrier PC2 to and from the second sun gear S2.The fourth clutch C4 is adapted to connect and disconnect the unity ofthe input shaft 10 and the first pinion carrier PCl to and from theunity of the output shaft 12 and the second internal ring gear R2.

The first brake B1 is adapted to fix and release the first sun gear S1to and from a stationary member, i.e., transmission casing. The secondbrake B2 is adapted to fix and release the second sun gear S2 to andfrom the stationary member. The third brake B3 is adapted to fix andrelease the unity of the second pinion carrier PC2 and the firstinternal ring gear R1 to and from the stationary member.

In the described first embodiment of the planetary gear typetransmission mechanism, forward five gear positions and a reverse gearposition of corresponding speed ratios can be established by selectivelyoperating the clutches C1, C2, C3 and C4 and the brakes B1, B2 and B3 asshown in FIG. 10 by "◯" marks.

FIGS. 11 to 16 are alignment charts at respective gear positions showingrelationship among rotation speed ratios of gear elements of bothplanetary gear sets to the input shaft 10. In these FIGS. 11 to 16, gearelements of each planetary gear set are positioned horizontallycorresponding to gear ratio of the planetary gear set, and vertical axesrepresent rotation speed ratio of the relevant gear elementsrespectively. The charts of FIGS. 11 to 16 are drawn based on the factthat, since the relationship of the rotation speeds of the sun gear, thepinion carrier and the internal ring gear in each planetary gear set haslinear relationship depending on gear ratio of the sun gear teeth numberand the ring gear teeth number, the rotation speed ratios of respectivegear elements can be directed to the intersections of a single straightline extending across the vertical axes and these vertical axes.

As can be seen from FIGS. 11 to 16, at all of the forward gearpositions, no gear elements is driven in the opposite direction withrespect to the input shaft. Also, as can be seen from FIG. 15, at thefifth gear position, i.e., at the most frequently used highest(over-drive) speed ratio, only the second internal ring gear R2 whichserves as the output gear element, rotates at higher speed than theinput shaft 10. At this fifth gear position, no gear elements except forthe second internal ring gear R2 is driven at a higher speed than theinput shaft 10. In addition, at the fifth gear position, the firstplanetary gear set G1 is held at idling condition and is not effectivefor power transmission. Therefore, only the second planetary gear set G2is active for power transmission.

As set forth, in the shown embodiment, since no gear elements willrotate at high speed or cause relative rotation at high speed,frictional resistance at the clutches and brakes can be reducedsubstantially and thus can enhance power transmission efficiency.Furthermore, since power transmission is effected only through thesecond planetary gear set at the fifth gear position which is frequentlyused in the normal driving behavior, gear noise can be reduced and powertransmission efficiency can be further enhanced.

In the shown embodiment, the fourth gear position can be establishedonly by engaging the fourth clutch C4 to directly connect the inputshaft and the output shaft, so that, it is not essential to engage thesecond brake B2. However, if the second brake B2 is held to be engaged,3-4 up-shift gear-change operation and 4-5 up-shift gear-changeoperation can be performed by releasing only one clutch or brake, and byengaging only one clutch or brake. This simplifies the gear-changeoperation and thus makes it easier.

The fourth gear position also can be established by engaging two of thefirst clutch C1, the second clutch C2 and the third clutch C3 as shownin FIG. 10 by "(4th)". This alignment chart at the fourth gear positionin this case is illustrated in FIG. 17.

FIG. 18 shows the second embodiment of the planetary gear typetransmission mechanism according to the invention. In this embodiment,the arrangements of the second clutch C2, the third clutch C3, thefourth clutch C4, the second brake B2 and the third brake B3 aremodified from that in the foregoing first embodiment. Relativeconnections among all of the constructional elements, however, areessentially the same as that in the foregoing first embodiment.Accordingly, the second embodiment can operate substantially in the samemanner as the first embodiment and can attain the same frictionaleffects.

FIGS. 19, 20 and 21 respectively show the third, fourth and fifthembodiments of the planetary gear type transmission mechanism of theinvention. Also in these embodiments, only arrangements of some clutchesand brakes are modified with maintaining essential connections among allof the constructional elements similar to the foregoing firstembodiment. Accordingly, substantially the same function as that of thefirst embodiment can be obtained.

FIG. 22 shows the sixth embodiment of the planetary gear typetransmission mechanism of the invention. In this embodiment, the firstclutch C1 and the third clutch C3 are adapted to connect and disconnectthe different gear elements to each other. Namely, the first clutch C1,in this embodiment, is adapted to connect and disconnect the unity ofthe input shaft 10 and the first pinion carrier PCl to and from theunity of the first internal ring gear R1 and the second pinion carrierPC2. Moreover, the third clutch C3 is adapted to connect and disconnectthe unity of the first internal ring gear R1 and the second pinioncarrier PC2 to and from the unity of the output shaft 12 and the secondinternal ring gear R2.

The alignment chart at each gear position for the sixth embodiment ofthe planetary gear type transmission mechanism is illustrated in FIGS.23 to 28. As can be appreciated from these figures, also in thisembodiment, substantially the same effects as those in the firstembodiment can be obtained. It should be noted that, though in the shownembodiment both of the first clutch C1 and the third clutch C3 arealtered from the first embodiment, only one of either the first clutchC1 and the third clutch C3 may be altered to obtain the same effects.

FIG. 29 shows the seventh embodiment of the planetary gear typetransmission mechanism according to the invention. The seventhembodiment is realized by modifying arrangement of the first clutch C1,the second clutch C2, the third clutch C3, the fourth clutch C4, thesecond brake B2, and the third brake B3 from the sixth embodiment. Therelative connections of the constructional elements, however, areessentially the same as that in the foregoing sixth embodiment and thuscan obtain substantially the same effects.

FIGS. 30, 31 and 32 respectively show the eighth, ninth and tenthembodiments of the planetary gear type transmission mechanisms accordingto the present invention. These embodiments are realized with onlymodified arrangements of the clutches and brakes. Therefore, relativeconnections of the constructional elements are essentially the same asthat in the foregoing sixth embodiment, and thus it can provide thesubstantially the same effects.

FIG. 33 shows the eleventh embodiment of the planetary gear typetransmission mechanism according to the invention. In this embodiment,the gear elements to be connected and disconnected to each other by thefourth clutch C4 are altered from the first embodiment. In addition, aone-way clutch OWC is provided in series with the second clutch C2. Inthis embodiment, the fourth clutch C2 is altered to connect anddisconnect the first sun gear S1 and the second sun gear S2.

With the arrangement of the eleventh embodiment, the relationship offriction elements to be engaged and gear positions established therebyis as shown in FIG. 34. At each gear position, gear elements rotate withthe relationship illustrated in FIGS. 35 to 40. As appreciated fromthese figures, also in the eleventh embodiment substantially the sameeffect as in the first embodiment can be obtained. In addition, sincethe shown embodiment incorporates the one-way clutch OWC, 1-2 up-shiftgear-change operation is performed easily by free-running of the one-wayclutch OWC.

Furthermore, in this embodiment, the required torque capacities of thefourth clutch C4 and the second brake B2 can be made smaller than thosein the first embodiment. Namely, regarding of the fourth clutch C4, ithas to transmit overall torque of the input shaft 10 only by itself inthe first embodiment, however in the eleventh embodiment, part of theinput shaft torque is loaded also on the first clutch C1 so that therequired torque capacity of the fourth clutch C4 will be approximately60% of that in the first embodiment. Also regarding the second brake B2,it has to be engaged at the third gear position as well as the fifthgear position in the first embodiment, however, in the eleventhembodiment, the second brake is to be engaged only at fifth gearposition so that the required torque capacity of the second brakebecomes approximately one half of that in the first embodiment.

It should be appreciated that such modification relative to the fourthclutch C4 and the addition of the one-way clutch OWC are applicable forany of the foregoing embodiments.

As set forth above, according to the present invention, the gearelements which rotate in the opposite direction to the input shaft atany forward gear position, can be successfully avoided. Also, at thefrequently used highest gear position, no gear element except for theoutput element will be driven at higher speed than the input shaft. As aresult, frictional resistance of the clutches and brakes can be reducedand thus improve the power transmission efficiency. Elimination of thegear elements rotating at high speed contributes to strength and cheapconstruction. Furthermore, since only one planetary gear set is activeat the highest gear position, gear noise can be suppressed and powertransmission efficiency can be more enhanced.

What is claimed is:
 1. A planetary gear type transmission mechanismcomprising:(a) an input member to be supplied rotation from a powersupply; (b) an output member for delivering rotation changed in speed atan selected speed ratio; (c) a first gear set including a gear elementconstantly coupled with said input member for rotation therewith; (d) asecond gear set including a gear element constantly coupled with saidoutput member for rotation therewith; and (e) friction means including aplurality of friction elements for determining power transmission routethrough at least one of said first and second gear sets for establishinga plurality of speed ratios between the input and output members; othergear elements of the first and second gear sets being coupled with eachother and the friction elements being arranged, in such manner that allgear elements of the first and second gear sets except for said gearelement constantly coupled with the output member rotates in the samedirection as that of the input member at speed less than the inputmember upon selection of any forward speed ratio.
 2. A planetary geartype transmission mechanism as set forth in claim 1, wherein the highestspeed ratio of said forward speed ratios is established in such mannerthat said second gear set is exclusively active for transmittingrotation of the input member to the output member.
 3. A planetary geartype transmission mechanism as set forth in claim 2, wherein said thehighest speed ratio is established by connection between said gearelement of the first gear set constantly coupled with said input memberand any one of gear elements of said second gear set for direct powertransmission of the input rotation to the second gear set.
 4. Aplanetary gear type transmission mechanism as set forth in claim 1,wherein said first gear set is a double pinion type planetary gear set.5. A planetary gear type transmission mechanism as set forth in claim 1,wherein said second gear set is a single pinion type planetary gear set.6. A planetary gear type transmission mechanism as set forth in claim 4,wherein said second gear set is a single pinion type planetary gear set.7. A planetary gear type transmission mechanism as set forth in claim 4,wherein said first gear set comprises a first sun gear, a first internalring gear, a first outer planet pinion gears and a first inner planetpinion gears meshed with each other, and a first pinion carrierrotatably supporting said first outer planet pinion gears and said firstinner planet pinion gears, said first outer planet pinion gears meshingwith said first internal ring gear, said first inner planet pinion gearsmeshing with said first sun gear, and said first pinion carrier beingconstantly coupled with said input member.
 8. A planetary gear typetransmission mechanism as set forth in claim 5, wherein said second gearset comprises a second sun gear, a second internal ring gear, a secondplanet pinion gears each meshing with both of said second sun gear andsaid second internal ring gear, and a second pinion carrier rotatablysupporting said second planet pinion gears, and said second internalring gear is constantly coupled with said output member.
 9. A planetarygear type transmission mechanism as set forth in claim 6, wherein saidfirst gear set comprises a first sun gear, a first internal ring gear, afirst outer planet pinion gears and a first inner planet pinion gearsmeshed with each other, and a first pinion carrier rotatably supportingsaid first outer planet pinion gears and said first inner planet piniongears, said first outer planet pinion gears meshing with said firstinternal ring gear, said first inner planet pinion gears meshing withsaid first sun gear, and said first pinion carrier being constantlycoupled with said input member,said second gear set comprises a secondsun gear, a second internal ring gear, a second planet pinion gears eachmeshing with both of said second sun gear and said second internal ringgear, and a second pinion carrier rotatably supporting said secondplanet pinion gears, said second internal ring gear being constantlycoupled with said output member, and said second pinion carrierconstantly coupled with said first internal ring gear.
 10. A planetarygear type transmission mechanism as set forth in claim 9, wherein saidfriction means comprises first, second, third and fourth clutches andfirst, second and third brakes, said first clutch connects anddisconnects the unity of said input member and said first pinion carrierto and from said first sun gear for selected speed ratio, said secondclutch connects and disconnects the unity of said input member and saidfirst pinion carrier to and from said second sun gear for selected speedratio, said third clutch connects and disconnects the unity of saidfirst internal ring gear and said second pinion carrier to and from saidsecond sun gear for selected speed ratio, said fourth clutch connectsand disconnects the unity of said input member and said first pinioncarrier to and from the unity of said output member and said secondinternal ring gear for selected speed ratio, said first brake connectsand disconnects said first sun gear to and from a stationary member forselected speed ratio, said second brake connects and disconnects saidsecond sun gear to and from the stationary member for selected speedratio, and said third brake connects and disconnects the unity of saidsecond pinion carrier and said first internal ring gear to and from thestationary member for selected speed ratio.
 11. A planetary gear typetransmission mechanism as set forth in claim 10, wherein said firstclutch is altered to connect and disconnect the unity of said inputmember and said first pinion carrier to and from the unity of said firstinternal ring gear and said second pinion carrier for the selected speedratio.
 12. A planetary gear type transmission mechanism as set forth inclaim 10, wherein said third clutch is altered to connect and disconnectthe unity of said first internal ring gear and said second pinioncarrier to and from the unity of said output member and said secondinternal ring gear for the selected speed ratio.
 13. A planetary geartype transmission mechanism as set forth in claim 10, wherein saidfourth clutch is altered to connect and disconnect said first sun gearto and from said second sun gear for the selected speed ratio.
 14. Aplanetary gear type transmission mechanism as set forth in claim 10,which further comprises a one-way clutch arranged in series with saidsecond clutch.